| Research Abstract |
Bacterial flagellum is an extracellular organelle. Therefore, most of the component proteins once synthesized in the cytoplasm have to be exported outside the cell through an export apparatus specific for flagellar proteins.
Among the component proteins in the apparatus, FliH and FliI proteins are regarded to work as a gate keeper, because the deletion mutants of those genes result in blockage of flagellation at the early steps.
We have developed a method to visualize flagellar basal structures from inside the cell. The method includes revised techniques for preparing osmotically-shocked cells, and the quick-freeze deep-ethch electron microscopy. We have succeeded in visualization of the flagellar C ring structure of Salmonella typhimurium.
Furthermore, in the course of developing the methods, we found a supramolecular structure resembling to flagellar basal body. Since it has a straight needle instead of the curved hook, we call the structure the needle complex. The needle complexes were purified, separated into components by SDS-PAGE, blotted onto nitrocellulose papers, and analyzed by the amino acid sequencer. The major component proteins were identified as PrgH, PrgK, and InvG that are known as pathogenic factors. These results strongly support a hypothesis that flagella and pathogenicity have the same origin.
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